Each SEG-Y contains typically a maximum of 1.1 GB of field recordings or a bit more than 50 shots. Typically, the file sizes range between 800–1000 MB. Where shot points have been skipped, the SEG-Y size is smaller.
These files are quality-controlled, meaning that noise tests, accidental recordings and duplicate traces have been removed and all relevant trace headers are set. The shot gathers have been prepared at the University of Helsinki, Institute of Seismology, during the year 2016.
The observer's notes and pole coordinates are also available as quality-controlled versions. Typical flaws in the original observer's notes include typing errors, wrong or impossible numeric values, and noise tests being erroneously flagged as recordings. A comprehensive erratum is available for all lines and can be downloaded under the OpenFIRE table view.
The samples are in IBM floats. The sampling interval is 2 milliseconds and the number of samples per trace is 15 000.
For the original, demultiplexed and correlated field recordings from Specgeofizika, see Raw data.
Finnish Reflection Experiment is a 2-D crooked-line seismic survey conducted using 4 to 5 Vibroseis sources per shot point. The pole interval of the survey is 50 meters. The nominal shot point interval is 100 meters, and each source and receiver group effectively corresponds to a single source or receiver placed in the midpoint of two adjacent poles.
The recording geometry is split-spread (asymmetric at the end of lines) with 362 active channels separated by a nominal group interval of 50 meters. This results in a nominal fold of ~90 for the entire survey.
The naming of files follows the general pattern
where the last two numbers separated by a dash specify a range of shot poles (source points). The shot gathers have been packaged so that around 50 shots should be included in each SEG-Y.
For example, the first 49 shots of FIRE 3-1 (shot points 1–94) are included in the file Fire_3_1_1-100.sgy, the next 48 (shot points 104–200) in the file Fire_3_1_101-200.sgy and so on.
The 3200-byte textual header follows a general format and is encoded in EBCDIC. Each row ends in an asterisk in column 80, and there are no linefeeds.
C1 FIRE Finnish Reflection Experiment 2001-2003 *
C2 Client : FIRE consortium: University of Helsinki, University of Oulu * C3 and Geological Survey of Finland *
C4 Contractor: Spetsgeofyzika, Russia *
C5 LINE <NO> <LOCATION> ; acquisition: <DATE OF ACQUISITION> *
C6 Source: Vibroseis: 4-5 vibrators, nominal shot point interval 100 m *
C7 Vibrator group length: 50 m *
C8 Sweep length 30 sec, linear upsweep 12-80 Hz *
C9 Fully correlated trace length 30 sec (Total listening time 60 sec)*
C10 Vertical stacking: 8 sweeps / shot point, correlation before stack*
C11 Recording geometry: Split spread, asymmetric at the end of lines * C12 362 active channels, group interval 50 m *
C13 Geophone groups: 12 geophones, group length 50 m *
C14 Number of samples: <SAMPLES> Sampling interval: <SAMPLERATE> *
C15 This reel contains the following field records (see obslogs): *
C16 <FLDR INTERVAL> *
C17 Number of traces in this reel: <NO TRACES> *
C18 Sourcepoint range: <EP INTERVAL> *
C19 CDP range: <CDP INTERVAL> * C20 *
C21 NOTE! trace header has the following non-standard fields: * C22 bytes 171-172 (grnors): pole of present detector * C23 bytes 173-174 (grnofr): pole of first detector in spread * C24 bytes 175-176 (grnlof): pole of last detector in spread * C25 *
C26 <MISCELLANEOUS NOTES> * C27 * C28 * C29 * C30 * C31 * C32 * C33 * C34 * C35 * C36 * C37 * C38 * C39 *
C40 END TEXTUAL HEADER *
In the 400-byte binary header, the following fields are set:
In the trace headers, set are the following fields:
The field record number refers to a row in observer’s logs.
The observer's notes have a number of comment lines in the beginning of the files (all starting with the symbol #) and then line by line the recording geometry and time for each shot.
The observer's notes have 9 columns, from left to right FLDR (field record identifier, bytes 9–12 in trace headers), FIRST (pole of first geophone in spread), LAST (pole of last geophone in spread), SHOT (shot pole), D (day), M (month), H (hour), MIN (minute) and S (second).
# Observer's notes for FIRE 3-1
# The numbers in columns 2,3,4 refer to peg numbers.
# Format string: "%8d %7d %7d %7d %3d %3d %3d %3d %3d\n"
# Fire 3-1 starts here
# FLDR FIRST LAST SHOT D M H MIN S
2 1 362 1 8 5 12 41 5
3 1 362 3 8 5 12 51 13
4 1 362 5 8 5 13 1 7
5 1 362 7 8 5 13 10 11
Even the quality controlled versions of the data may contain errors. A comprehensive erratum is available for all lines and should be always consulted before using the data.
No attempt has been made to remove or mute noisy traces.